I am not a LyX user, but I would strongly suspect this depends on which document class you are using. Can you provide that information?
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Andrew SwannApr 10 at 8:20

2 years and a half later, not really! ;)
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Ricky RobinsonApr 10 at 10:35

I don't understand your comment. Looking at the answers below the low level \and is an appropriate solution for article but not for amsart where mark up of multiple authors is radically different.
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Andrew SwannApr 10 at 12:09

My question is from September 2012. Thank you for your interest, but... I've moved on since then! :D
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Ricky RobinsonApr 10 at 14:13

Ah, I see - I didn't look at the edit history. However, questions and answers here are meant to be of use to future visitors, so I think it would be good if the question stated which set of document classes you wish answers to apply to.
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Andrew SwannApr 10 at 14:22

choose from the paragraph menu author. Then insert the name of author_A, then choose a footnote from the menu and insert in this footnote an URL (from insert->URL) and after elaving the url window the University as normal text. Now Leave the footnote window and insert with Ctrl-L the LaTeX code (Evil Red Text)
\and. Now do the same for author_B and author_D without leaving the author field.

Thank you. I did as you said, but the \and operator is hiding everything there is before. I mean, in the resulting pdf file, I only see author C. Anyhow, the footnotes are appearing in the bottom of the page, which is not what I was looking for. They should be right below the author name, right? Either all together, or more neatly below the corresponding person.
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Ricky RobinsonSep 19 '12 at 16:44

then use a tabular for every author for name and email.
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HerbertSep 19 '12 at 21:58

I can't see the reason for using footnotes. Does the question state anything like that? Or do you mean to reference them? In which case I would use a bibliography, such as Bibtex
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chwiSep 21 '12 at 13:45

A \footnote in the authors part is automatically converted into a \thanks command which should be used by default!
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HerbertSep 21 '12 at 14:24

Welcome to TeX.SX! This syntax is slightly wrong I'm afraid, it should be Author one \and Author two \and Author three. The \and command does take an argument, it is just a separator.
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Torbjørn T.Apr 2 at 18:08

(I meant to say 'does not take an argument'.)
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Torbjørn T.Apr 3 at 5:34